1. Field of the Invention
The present invention relates to an inkjet ink composition, and in particular, to an inkjet ink composition containing a polymeric compound having an acidic group that suppresses sedimentation of white ink and prevents clogging of inkjet nozzles.
2. Description of the Related Art
Essential functionality of white ink is high masking efficiency and tinting strength, because white ink having a lower masking potential, when printed on a colored medium, often results the color of the printed medium appearing through the ink and deterioration in color reproducibility.
Thus, white ink is applied first, and then, other inks of different color are applied thereon. Thus, the amount of white ink used is larger than those of the inks of other colors, and demand for white ink has been constantly growing. Screen printing is often used for application of white ink, but this method has problems in that it is only applicable to printing on flat surfaces and it is difficult to draw fine detail.
On the other hand, inkjet printing ink, which is more convenient and compact than ink in conventional printing methods, and allows printing on three-dimensional media because it is non-contact printing, is becoming more and more popular.
It is possible to overcome the problems of conventional screen printing, and thus, to print images on 3D media and fine detail, by coating with white ink using an inkjet system.
However, the viscosity of the ink used in the inkjet system needs to be low. Accordingly, white inkjet inks have problems of low dispersion stability and easier sedimentation of the pigment. Because the sediment pigment often coagulates, resulting in clogging of inkjet nozzle, blurring of printing image, or uneven printing, there exists an urgent need for a white inkjet ink of low viscosity with superior dispersion stability.
A method of specifying the specific gravity of silica and alumina, and adding an acidic group-containing polymer dispersant was proposed for preparation of white inkjet ink improved in dispersion stability (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2004-59857), but this method is difficult to stabilize and difficult to produce. Thus, white inkjet ink having a favorable dispersion stability is not yet available.